Braun tube



B. ENGELS BRAUN TUBE Nov. 19, 1940.

Filed April 22, 1938 @m/mf @fm v @Kw Patented Nov. .19, 1940 BRAUN TUBEBernhard Engels, Waldenburg-Altwasser, Schlesien, Germany ApplicationApril 22, 1938, Serial No. 203,549 In Germany November 5, 1935 2 Claims.

ln television practice there are used for the reception of the imagecathode ray oscillographs in the form of the so-called Braun tube. Thisconsists of a Vdischarge tube which is suitably evacuated until almostabsolute vacuum, with a cathode connected on to negative potential asthe source of the rays, an anode usually earthed, a diaphragm alsoearthed, allowing the passage of a narrow beam of rays, one or moredeflecting condensers or deecting coils and a luminous screenperpendicular to the path of the cathode rays, which is arrangeddirectly in front of or on the inner surface of the end of the tubeoppositethe cathode.

Such Braun tubes were at first made com pletely of glass and this in theusual Way by blowing in a mould. In this way, however, such tubes couldonly be made up to limited dimensions determined by the workingconditions applying with this method of shaping, and it was hardlypossible to go beyond 20 cm. in the diameterof the reception end of thetube having the form if an Erlenmeyer bulb. This limitation, however,carries with it a limitation of the images received on the surface givenin this way, with respect to their size, vwhich limitation is veryundesirable.

A further disadvantage of the blown tubes lies in the fact that in theproduction by blowing the glass is never plane-parallel but showsuctuations in thickness and certain distortions.

It has already been proposed if even without recognition of thepossibilities thereby given for the enlargement of the receptionsurface, to make such Braun tubes in several parts instead of blowingthem in one part out of glass, that is, to subdivide them into thejacket and the end surface when the jacket for the purpose of avoidingsurface charges and for the electric screening of the cathode raysconsists preferably of a metal `tube of suitable shape, as a ruleearthed, and which is joined vacuum-tight with the end consisting ofglass upon which is applied the receiving luminous screen.

It is known to avoid the distortions of the image resulting from thecoating of the end itself with the luminous substance in the case ofblown and thus more or less curved ends, by forming the end by aplane-parallel mirror glass plate.

While with tubes constructed in this Way independence is attained oflimitations in size caused by the peculiarities of the process ofshaping the vglass by blowing, yet there arises the other difficultythat the flat plate closing the tube may not be suiiiciently resistanteven with (Cl. Z50-164) the usual diameter of the end in the order ofsize of about 20 cm., in view of the high pressure stresses occurringand which in practice may amount on account of the almost completevacuum in the interior of the tube, to l kg. per square 5 cm.Consequently with the known tubes either a plurality of plane-parallelplates have been superposed or a plate has been supported by a metalgrid. This has naturally as a result a less sharpness or definition ofthe image to be 10 reproduced, in consequence of the great thickness ofthe multiple plate or of the arrangement of the grid.

In order to obviate this difficulty to some extent at least with tubesof the `hitherto usual 15 end dimensions, it has been proposed to closethe tube by a simply curved cylindrical glass disc the axis of which isperpendicular to the axis of the tube. Whilst this arrangement presentsa certain increase of the resistance to pressure, yet 20 in this thepressure stresses are still directed comparatively unfavourably; thereis furthermore given in this arrangement a diftlcult construction of thejoining of the disc with the metal tube on a curved surface, which canonly be 25 made absolutely vacuum-tight with difficulty.

According to the invention, it is proposed to use for closing the tube,which may consist of glass or metal, a spherical cap-shaped mirror glassplate of flat curvature, ground and pol- 30 ished plane-parallel, whichrests tightly along a flat and/or circularly curved-and thus in bothcases easily worked-surface on a corre sponding surface of the tubejacket and is thus joined thereto. An absolutely secure vacuum- 35 tightclosing can here be'attained either by cementing or by fusing, accordingto recent processes, with the tube wall. Such a closing of the tube by aspherically curved mirror glass plate represents the best form ofconstruction for taking the pressure stresses, it being possibleaccording to the diameter of the end of the tube to select the curvatureof the mirror glass plate bearing in mind the pressure stresses to betaken thereby, i. e., to make the curvature so great as 45 is necessaryfor taking these stresses.

Thus it is possible as long` as the diameter of the end of the tube isnot too great, to curve the mirror glass plate forming the end only soslightly that the rise of the curvature in the 50 unloaded conditionamounts to only a few millimetres, and is consequently so small thatafter the insertion of the plate and the evacuation of the tube, theplate, under the influence of the external pressure flexes so muchinwardly that 55 in the nnal condition it has a level surface. The

increase in the circumference of the plate thereby occurring is soslight that it is practically immaterial and can be easily taken up bythe 5 material of the jacket.

An embodiment in principle of the invention is shown on the annexeddrawing in which, with the omission of the electrical parts, Fig. 1represents a longitudinal section through the end l part of the improvedtube, at the same time illustrating on the left-hand andon the righthandhalves, different possibilities for the tight uniting of the closingplate with the tube, and Fig. 2 is a fragmentary sectional view of atube l5 showing the end plate in its initial andl nal positions.

In Fig.` 1, a represents the jacket of the tube, which Vfor exampleconsists of metal, whilst b indicates the end piece, consisting of a capor 20 dome-shaped mirror glass disc, uniformly curved all over andground and polished plane-parallel, the radius of curvature of which isapproximately equal to the greatest diameter of the cap or dome and overwhich is applied in known 25 manner the luminous screen if this is notarranged independently thereof in front of the end of the tube.

The tight connection of the mirror glass plate with the jacket takesplace according to the 30 embodiment of the invention represented on theright-hand side of Fig. 1 by the edge of the plate being groundcircularly so that there is given a surface c directed substantiallyradially to the curvature of the plate and which with the interposing ofa suitable jointing material d rests on a correspondingly curvedcounter-surface e of the end f of the jacket made in flange form.

This counter-surface can preferably also be provided with grooves g andsuch grooves can also 40 be ground into the edge surface of the mirrorglass plate in order in this way to still further ensure thevacuum-tight connection. In addition, there can also be arrangedjolnting material in the space h between the end of the 45 widened-outflange f and the outer surface of the mirror glass plate. A ring i isfitted round the flange, preferably under tension.

The embodiment shown on the left-hand side of the ngure diers from thatpreviously described only by the form of the Joint surface; here theedge of the mirror glass disc is resolved into two surfaces at rightangles to each other, v o1' which the one c1, which is vertical in the 5gure, is radially curved, whilst the other, shown horizontally in theiigure and indicated by c2,

is fiat, so that the corresponding counter-surfaces g1 and a2 can besimultaneously produced on the flange f by a very simple working procl0ess. Here, again, there are preferably provided additional grooves e inthe supporting surfaces of the flange and/or of the disc and possiblyalso amount, not shown in the figure, partially overlapping the plate,although this in itself is not necessary on account of the pressureacting on the plate in the direction from the outside towards theinterior.

Fig. 2 represents in exaggerated form an end plate b having an initiallyspherical curvature mounted over the end of the tube body a. Subsequentevacuation of the body of the tube causes the end plate b to assume itsfinal level position which may be that indicated in dotted lines. Whilein the form shown the flnal position of the end plate is planar, it willbe appreciated that any desired final curvature may be attained, so longas it is caused by distortion of a plate having initially sphericalcurvature.

What I claim is:

l. A Braun tube, including a jacket containing gas under sub-atmosphericpressure, an end member seated in said jacket having plane parallelsurfaces, one of which is coated, and sealing means surrounding said endmember, said end member being formed as a spherically formed plate andbeing suiliciently flexible to be bent by the diilerential pressurebetween the interior and exterior of the jacket into a plane positionand being held in its plane position by the pressure diierence betweenthe exterior and the interior of said jacket.

2. A Braun tube in accordance with claim 1 in which the peripheralsurface of said end member is parallel to its-seat in said jacket and ismaintained in parallelism by the pressure of the atmosphere.

BERNHARD ENGELS.

